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Abstract

Aptamers, which are in vitro-selected functional oligonucleotides, have been employed to design novel aptasensor due to their inherent high selectivity and affinity compared to traditional biorecognition elements. This report presents a novel aptamer biosensor for determining the endocrine disrupting compound (EDC), 17β-estradiol (E2), which was constructed from a SELEX-synthesized 76-mer biotinylated aptamer for 17-estradiol incorporated in a dendritic generation 1 poly(propylene imine)-polythiophene (G1PPT-co-PEDOT) star copolymer-functionalised Au electrode via biotin-avidin interaction. The sensor platform and aptasensor were interrogated with scanning electron microscopy (SEM), FTIR, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and square wave voltammetry (SWV). The kinetic parameters of the sensor platform were determined by modelling the [Fe(CN)6]-3/-4 (redox probe) Nyquist and Bode impedimetric spectra to the appropriate equivalent electrical circuit. The EIS spectra shows that at low frequencies (100 mHz) when the electronics of the electrode systems are only minimally perturbed the AuG1PPT-co-PEDOT nanoelectrode exhibited greater semi-conductor behaviour (higher phase angle value) than AuG1PPT due to the incorporation of charged functionalized dendrimer. However, the Bode plot also shows that the charge transfer dynamics of the nanoelectrode can be frequency modulated. The biosensor response to 17β-estradiol was based on the decrease in the SWV current as the EDC binds to the ssDNA aptamer on the biosensor. The dynamic linear range of the sensor was 0.1 – 100 nM. These initial studies also showed that the aptamer used in this study was very selective to, and reproducible for, 17-β-estradiol.
Keywords: Functionalized dendrimer, conducting polymer, 17β-estradiol (E2), star copolymer, SELEX, endocrine disrupting compound, DNA aptamer, electrochemical impedance spectroscopy,